<template>
    <ul class="list" >
        <li class="item" v-for="item of letters"
            :key="item"
            :ref="item"
            @click="handleLetterClick"
            @touchstart="handleTouchStart"
            @touchmove = "handleTouchMove"
            @touchend = "handleTouchEnd"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
    import BScroll from 'better-scroll'
    export default {
        name : 'CityAlphabet',
        props:{
            cities:Object
        },
        data () {
            return {
                touchStatus : false,
                startY : Number,
                timer : null
            }
        },
        updated () {
                this.startY = this.$refs['A'][0].offsetTop
        },
        computed : {
            letters () {
                const letters = []
                for (let i in this.cities) {
                    letters.push(i)
                }
                return letters
            }
        },
        methods:{
            handleLetterClick (e) {
                this.$emit('change',e.target.innerText)
            },
            handleTouchStart () {
                this.touchStatus = true
            },
            handleTouchMove (e) {
                if(this.touchStatus){
                    if(this.timer){
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        const touchY = e.touches[0].clientY - 79
                        const index = Math.floor((touchY - this.startY) / 20) 
                        if (index >= 0 && index < this.letters.length){
                            this.$emit("change" , this.letters[index])                        
                        }
                    } , 16)
                    

                }
            },
            handleTouchEnd () {
                this.touchStatus = false
            }
        }
    }
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
    .list
        display:flex
        flex-direction:column
        justify-content:center
        position:absolute
        right:0.08rem
        bottom:0
        top:1.58rem
        // background:red
        .item
            text-align:center
            line-height:.4rem
            color:$bgcolor
            // list-style:none
</style>

